Concentric hot plate



CONCNTRIC HOT PLATE' A.

' Filed oct.- 20, 1927v l www = v ATTORNEY v .l devices and PateffedMu.. 19,*i 1929. l

'UNlT-'ED STA i Application led ctober 20, 1927,`Serlal No. 227,445, andin GreatBritainJ'anuary 28, 1827.

I `My invention-relatesv to electrically heated units.. l

An object of my invention is to provide a I relatively simple,-highlyeilicient,` flat elec-v 1 tric-heatin unit, the surface of which shallbe-uniform y heated.

Another object of my invention is to pro- Vide a two-part heater thatVshall embody 10 means for maintaining the two parts in.

proper operative positions vrelatively to each other and for reducingthe heatvilo'w therebetween.

In practicing mylinvention, I iprovideam inner heating unit-embodying aplurality of metal-encased tubular heatingA elements embedded lin -asubstantially' circular-mass of cast metal having a i peripheralshoulder thereon and an outerV annular heatin unit 20 embodying aplurality o f metal-encase tubular elements embedded in an annulus ofcast metal. A screw-threaded stud extends into the central mass of castmetal and cooperates with a metal spider to hold the'two units inJ 26proper operative position in one plane,

In the single sheet of drawings: Figure 1 1s a-vie'w, in section on theline I--I of Fig. 2, of a device embodying myinvention, and v i 3 I Fig.2 isa top plan view thereof.l

A two-part heater embodies an inner heating unit 11 and an outer heatingunit 12, the two parts being concentrically located.`

The heating unit 11 embodies a pair of metal-encased tubular heatin`elements 13 i L and 14, each bent to substantlally U-shape,

as is shown moreparticularly in Fig. 2 of the drawing, the end`-portions thereofbeing bent down- 0 wardly out of the plane of the ,otherpart of the heatin elements. f

Each of bodies an outer metal casing 15, a helix -16 of resistor wirelocated therein and held'tight- 4,5 ly by a crystalline mass 17 ofelectric-insulating material consisting of magnesium hydroxide or oxide.The method of making these heating elements is more lparticularlydisclosed and claimed in my Relssue Patent 5o No. 16,340.

Briefly, the method therein described comprises winding va resistor wireinto helical particularly to electric-heating,

'sired shape,

j resistance,

and located. in a ysingle plane,`

.the heatlng units 13and-14 emcmusrIAN n. Maxim. or BRooxLYN, NEW Yonx.l

form, surrounding the hellx of resistor wlre p `or holds the resistorhelix -within the metal.

tube, which tube may then be bent to any desuch as that shown in thedrawings. As the mass 17 ofmagnesium hydroxide or oxide, is acrystalline mass that provides a heat-conduetin path from the resistorto the metal tube, '0

so that there is a relatively small temperature gradient only betweenthe re'- sistor and the outer surface of the metal tube. -The twoheating elements `13 and 14 are then located in a suitable mold and heldby very low thermal I molding nails or othersuitable means, to per- V lmit of casting therearound a mass 18 of'metal which) is preferably madeflat and circular.

A peripheral shoulder portionv 19 is provided 4 at the upper edgethereof, and the upper surface thereof is smoothed and polished, as maybe considered necessary or desirable.

The outer annular heating element 12 embodies a plurality of heatingelements 21 and 22 which are bent to substantially circular shape landwhich are located in the same plane. The end rtions thereof extenddownwardly out of thls plane.

The vmethod of construction of the heating elements 21 and 22 is thesame asV has been hereinbefore described for the heating elements 13 and14. c l

An annulus-23 of cast metal is provided to embed the heating units 21-a-nd`22, the method of supportingcfthe heating velements 21 and 22during the casting operation being well known and, therefore,unnecessary to describe in detail.

The annulus 23 is provided with a plurality Y of peripherally spacedlugs 24 extending radia ly inward and located a slight distancemetal-encased tubular '1 against the 430 The heating elements 45irrespective of whether the two heatin below the upper surface oftheannulus 23. The

" innerfaces of the lugs 24 arev adapted toengage the outer peripheralsurface of the circu- 18 to cast metal, and the upper suri face-of thelugs 24 i`s adapted to -fit below the lar mass shoulder portion v19 ofthe mass 18 ofecast .metal. ,Y

A-screw threaded rod or stud 25 is located coaxially with the twoheating units and more particularly with the screw threaded openingbeing provided in the masses of cast metal, -a

member 18 to receive the upper end ofthe stud.A Aspider or 'skeletonframe 26 is provided, having a central ,portion and a plural- 1 5 ity of'arms extending radially outward therefrom. The central portion has thestud 25 ex-` tending therethrough, and the' outer ends of the armsoperatively engage a portion of the lower surface of the annulus 12,being pressed 20 thereagainst by a nut 27 having screw threadv edengagement on the stud and pressing central portion of the member- 26.In order to reduce the heat iow from the l mass 23 ofcast metal to thespider 26, I prefer 25 to cast the member23 withja recess 28 in itslower surface, providing-relatively narrow ridges of metal at theedgethereof, whereby the area of surfacelin actual engagement is reduced toa minimum.

inbefore described, are substantially standard articles 'and Iv havetherefore,

any additional details of construction, lsuch as the terminals and theterminal construction f provided therefor.

' As has beenherembefore stated, the two heating elements13 and. 14 inthe central member y11 shape and are thenlocated in; such position [40that Vthey extend oppositely-to each other, as

is. shown more particularly in-Fi 2 of the drawing. This locationpermits o lobtaining a substantially uniform temperature oftheentire'upper surface of the central heating unit,

ments 13 and 14 are connected in series-clrcuit relation and energizedfrom a source of electric energy of a predetermined voltage to pro- Ivide a low heat; whether only one ofthe heatl ing elements is energized,or'whether both heating elements are-energlzed while connected inparallel-circuit relation; Such connections and `method of control arewell known inthe art and it is, therefore, considered unnecessary todescribe these in greater detail.

' When itis desired to thus connect two heating elements indifferentrelatlons to provide` aselective .plurality of temperatures, it isdesirable, if not necessary, that the lengths ofthe resistor be thesame, and the construction, shape and location of the heating elements13 and 14 are such as to effect the desired result; namely, uniformheating of the operative surface of the unit 11 under all condi- Itionsof operation. l

13,14, 21 and 22 here- I not described v are each bent to .substantiallyU- ele- It is possible also to make the lengths of the heating elements2l and`22 the same, so that they also may be connected in a plurality ofrelations, inthe manner described above.`

Itis, of course, obvious `that it is possible to energize the heatingelements-13 and 14 either individu ally or simultaneouslywithout, at thesame time, energizing the heating elements 21 l and 22, -This permits ofadapting the heater lto the size ofthe cooking utensil being-employed atany time. y

v The cooperating shoulder and lugs'onl the inner and the outer heatingunits provide a very simple means, which in -combination l with thespider andscrew threaded stud', will maintain the two heating units inproper operative positions relatively to each other in both a radialplane andin a plane parallel to the operatingsurface ofthe heater.Simultaneously, the relatively small surface area of contact between thetwo-heating units and, 'more particularly between the masses of .cast

metal, tends to reduce the flow of heat therebetween to a-minimum.

Various modifications-may be made in the device embodying my inventionwithout departing from the spiritandfscope thereof, and' e I. desire,therefore, that only suchlimitatins shall be 4placed thereon as areimposed vby the prior art or are specifically set forth in the appendedclaims.

I claim as my invention;

V1. A multi-unit heater comprising a central i circular mass ofcastmetal having an outer over-hanging shoulder portion and a metalencasedtubular heating element embedded in the castmetaL-and an outer annularmass of cast metal embodying a plurality of inwardly-extending portionto locate the annular mass in proper operative position both'axially andradially lugs fitting below said shoulder relatively to the centralmass, and a metalencased tubular heating element embedded in saidannular mass.

2. An electric heater comprising a central:

substantially circular mass of cast metal emmass of metal, and a nut onsaid rod for hold- 125 .i I

ing the skeleton frame in close operative engagement with the'annularmass of metal, the lugs of which are-thereby pressed against theshoulder on the central mass of metal.

3. An' electric heater comprising a central '180 l 1,705,702 v l -v 3vcircular unit andan outer annular unit, each units apart andv reduceheat .ow therebe-v unit embodyingameta1-encased tubnlar heattween.` l Al' ing element, and a mass of cast metal em- Intestimony Wl1ereof,Ihavehereunto sub- 10 beddingthe same, and the annular unit hav-- scribed myname this 10th day of October, 5 ing a plurality of lugs integral withthe cast 11927.

. metal and extendingradially inwardly to env gage' the circular unit tospace the heating CHRISTIAN B. BACKER. Y

